Rotary ore-reducing kiln



Dec. 5, 1961 M. E. RoUAux 3,011,772

ROTARY oRE-REDUcING KILN Dec. 5, 1961 M. E. RoUAUx 3,011,772

ROTARY ORE-REDUCING KILN Filed July 14, 1959 2 Sheets-Sheet 2 nited States Patent 3,611,772 Patented Dec. 5, i961 are 3,011,772 ROTARY ORE-REDUCING KILN Marcel Eugne Rouaux, 122 Rue Robespierre, Saint-Etienne, France Filed July 14, 1959, Ser. No. 827,062 Claims priority, application France July 24', 1958 3 Claims. (Cl. 26S-24) This invention relates to kilns. Kilns are known which include a sloping rotary body and a cylindrical jacket extending coaxially therewith over the entire periphery of the rotary body, the ends of these components being substantially in registry. Such kilns further include a cylindrical roasting chamber coaxial with the jacket at its upper end and opening into a chimney for the exhaust of the smokes, as well as means for feeding ore into the roasting chamber at its upper end and means for introducing continuously a large amount of cold air into the lower end of the jacket so as to constrain said air to rise in counter-flow relationship with the downward movement of the ore subjected to gravity. Further included are means for introducing reducing gases into the lower end of the kiln body and means for constraining the air reaching the upper end of the jacket to return directly into the upper end of the 4kiln body in order to burn the residuary gases formed in the kiln body by the reduction of the ore through the reducing gases.

Such kilns require, in principle, gauged ore particles. The conditions governing the reducing gases in these kilns, however, are not rigid. lf required, the degree of reduction can be limited. Said kilns are therefore suitable for the more or less complete reduction or moist material laden 'with deads, They are thus capable oi playing an important part in industry.

My present invention has for an object improvements in the construction oi such a kiln, so that it may be possible to reduce therein all kinds of ores, by introducing into it gases suiting the reduction to be executed both as concerns grade and amount. To this end, there are provided:

A jacket surrounding the entire wall of the kiln, so as to recycle towards the central section the excess heat from the ends of the rotary kiln;

A suitable partitioning of the inner chamber of the kiln which disperses the suiciently subdivided ore inside the stream of reducing gases, while means are provided to insure the conveyance of the reduced products as soon as they are sufliciently nodulous;

A feature whereby the kiln is closed and adapted to operate under pressure, rotary fluidtight joints being provided or the introduction and extraction ot the solid and gasiform material used during treatment. It is quite pcssible to produce inside the kiln the heat energy required for reduction upon partial combustion of the reducing gases by the oxygen forming a` combustive material. Under such conditions, it is possible to recycle the residuary gases after regeneration thereof, as far as their chemical composition is concerned;

Means are provided for heating through partial combustion of the gases in dilerent sections of the kiln, which allows consequently only a clean reducing reaction.

l have iilustrated by way of example in the accompanying drawings a preferred embodiment of such a rotar] reducing kiln. in said drawings:

FIG. l is a View of the kiln in longitudinal axial crosssection, associated with a diagram showing the auxiliary apparatus required for its operation.

FIGS. 2 and 3 are, on an enlarged scale, longitudinal axial cross-sections of the ends of the kiln, facing the input of the raw material and the output of the treated material respectively.

FIG. 4 is a cross-section rough line 4 4 of FIG. l.

ln said kiln, the wall 2 of the ore-treating chamber is entirely surrounded by a hea -insulated metal casing 3 forming with the wall 2 an annular jacket 4 through which ows a large fraction of the reducing gases. The latter are introduced in the direction of the arrow 5 (FIGS. 2 and 3), through the rotary joints 6 and 7 (FIGS. l to 3), located at the opposite ends of the rotary kiln. The gases entering at 6 and 7 are heated through their contact with the wall 2 which should be made of a heatresisting steel or the like high grade material and it may also be provided with recesses for the passage of gases inside it.

The gases passing through the annular jacket 4, between its inner wall 2 and the outer casing carry along with them the heat removed from said wall 2, so as to recycle said heat into the central section of the rotary kiln. The reducing gases introduced into the jacket 4 through the rotary joints 6 and 7 enter the central section of the kiln in registry with the different compartments 17 through the ports 20 through which also extend the noz- Zies l5 injecting oxygen into said compartments. Furthermore, a fraction of the reducing gases is shunted o the jacket in registry with the output end of the final product obtained, the desired fraction of the gases being directed towards the inside of the kiln through the channels 8 controlled by the valves 9, so as to remove entirely the heat carried by the iinal products obtained throughy a counter-current operation before said products are conveyed away, out of the kiln.

Oxygen produced for instance in an oxygen-producing plant it) is injected after compression into the kiln through the rotary joint l2 (FGS. l and 3) into the distributing tube i3 made of stainless steel or like metal which cannot be attacked by oxygen. To which tube 13 are connected annular pipes 14 (FiG. l) extending peripherally round the outer casing 3 and by means of which the oxygen is fed across the jacket into the inside of the kiln through the above-mentioned nozzles 15 each controlled by a valve i6. Said injection of oxygen is limited to the amount of combustive material required for the production of heat energy, by a partial combustion of the gases, with a view to insuring an optimum reduction of the ore. lt is sutlicient, as a matter of fact, to eiect a partial combustion of the reducing gases, for instance of the order of 18% of the total volume of the gases used or the reduction of iron ore, and to heat properly the mass of unburnt reducing gases.

The partial combustion and heating of the gases may be produced in the annular transverse compartments i7 of a suitable size, out of which the gases are fed into the axial portion of the rotary kiln, through a continuous or discontinuous line of tuyeres l.

ln FiG. 4, which is a transverse cross-section of the rotary kiln extending through a heating compartment, it is apparent that the oxygen-feeding nozzles 15 open into venturi-shaped members 22, so as to produce an innammable gasiform mixture of the oxygen with a fraction of the reducing gases, the remainder of the reducing gases lowing outside said members 22.

During the reduction of iron ores eected, by way of example, at a suicient temperature of say 1,100 to l,250 C., it is possible to provide for reduction at each operation of a large fraction of the gases, said fraction depending on their composition chiey as to hydrogen and carbon monoxide. Said fraction may be for instance of the order of 35 to 40%, so that the gases may be recycled 2.5 to 3 times after their chemical regeneration outside the kiln as obtained by conventional means say through absorption of their carbonic gas. Under such conditions, about 6% of the reducing gases are burnt at each passage of the gases through the kiln.

The kiln which is entirely closed may be subjected to 'an internal pressure, whereby its treating capacity is obviously increased. Y

The thermal eiiiciency of the rotary kiln may reach a very high figure and the casing 3 may in fact be outwardly heat-insulated. By way of example, the heat eiciency of such a rotary kiln may be higher than that of a blast furnace.

The comminuting of the ore increases the speed of reduction. Furthermore, it is essential to disperse in an active manner the particles inside the body of gases passing through the rotary kiln. To this end, may resort to the arrangement 50 described in my French patent tiled on May 5, 1958 and entitled Arrangement for Dispersing a subdivided Material Undergoing Treatment lnside a Rotary Kiln, said arrangement consisting or pro-V viding the inner refractory walls of the kiln with helical channels for collecting in a continuous manner during the rotation of the kiln a sufficiently large fraction of the pulverulent material undergoing treatment, conveying same and raising it again so as to pour it finally in sub stantially vertical showers in as largeamounts as possible into the inner end of the rotary kiln.

This arrangement insures furthermore a rapid transfer of the nodulous material formed during the reduction in the form of metal Sponges inside a rotary kiln with a reduced slope and the rotary speed of which is practically of the magnitude of the speeds which are usually obtained in rotary kilns serving for the production of cement.

In the embodiment illustrated in the drawings (FIGS. l and 4) the kiln encloses a succession of compartments separated by thresholds in the shape of venturis which produce an advantageous deposit of dust.

At the end of the kiln into which the ore is introduced, the transverse compartments 2d allow a useful exchange of heat between the gases andthe ore to be treated and also the inner wall 2 of the jacket.

The compartments 23 near the middle of the kiln are fed with gases, which have not yet been used, in amounts which are adjustable independently in each compartment and which have been brought to the desired reduction temperature in each chamber with a View to obtaining a reaction as speedy as possible at a temperature which may be defined by way of example as ranging between 1,100 and l,250 C. for the reduction of iron ore through a gas with high contents of hydrogen.

Y Near the output end of the treated material, the compartments 24 allow again the desired heat exchange between the gases, the treated material and the wall 2 of the jacket.

The ore to be treated is fed through a double sluice into the pipe 25 and the chamber 26 (FIG. 2) forming the rotary joint 27. The ore is removed from said chamber 26 by the conveyor worm 2S rigid with the shaft 29 resting freely in a bearing 36 carried inside the kiln and in a stutling box bearing 31 beyond which the outer end ofthe shaft is driven through the agency of a sliding joint 32 of the cardan type or the like, by a motor which is not illustrated.

The ore enters the kiln in the direction of the arrow 33 through the chamber 34 inside which is arranged a propeller 40 urging the ore into the kn. After passing through the successive series of compartments 21, 23 and 24 generally designated as compartments 17, the treated ore .enters the output port 11 towards which it is urged by the propeller 3S arranged in the terminal chamber 36.

The treated ore is collected at said output end by the worm 37 (FIG. 3) which is mounted and driven in the same manner as` the worm 28 and which urges the treated ore outwardly and downwardly, for instance into a double sluice arrangement through a channel 38 connected with the chamber 39 forming the rotary joint 41.

The gases which have passed through the kiln escape in the direction of the arrow 42 through the rotary joint 43 illustrated in FIGS. l and 2.

The rotary kiln is designed and operates in a manner such that its ends may remain as cold as possible Without however causing a dew point to he reached ahead of the kiln for the gases which have served for operation.

YThe highly reducing gases may be obtained in any suitable manner and a gas-feeding pipeline 44 (FIG l) may convey under pressure natural gas for instance into a plant 45 for catalytic cracking in the presence of oxygen under a pressure of say 20 kgs. per sq. cm. A pipe 46 feeds the gases produced to the rotary joint of the kiln. A shunt pipe 47 taps off said pipe 46 the amount of gas whic is to be injected into the furnace jacket through the rotary joint 6 at the ore input end.

As described hereinabove, it is necessary before' recycling the gases to regenerate them as far as their chemical composition is concerned. To this end, the gases issuing from the rotary joint 43 are fed through the pipe Q18 connected with the rotary joint 43 to an arrangement 49 provided for the separation of dust, water and carbonic gas. From time to time, it is desirable to remove the inert mass of nitrogen and argon which is always reforming. This removal may be obtained in a discontinuous manner by a set of bottles 5l which are inserted in turn in the circuit. The regenerated gases are then recycled through SZ.

The rotary kiln described, although it does not provide for a roasting of the ore before reduction thereof, is capable of many applications. Working with rich and multiform reducing gases, it reduces at a high speed iron ore, whether clean or otherwise, crushed into particles of a size of about 0.5 mm. lt is necessary to completely dry the ore before its introduction into the kiln.

By way of example, various additions to the ore may be made, in particular alkaline or alkaline-earth'oxides may be incorporated, not only to purify the metal, but also for furthering the migration of the iron particles into the metal sponge obtained and the formation of metal cakes of a size such that it is an easy matter to recover them in a subsequent stage through a crushing and magnetic sorting.

It should be mentioned that the daily production of the rotary kiln described measured with reference to the useful volume unit of the kiln is far larger than that of rotary kilns using subdivided coal distributed in the charges of crushed ore. Furthermore, it isV obvious that my improved rotary kiln eneloses a single atmosphere of an adjustable composition instead of two atmospheres, as in the case of rotary kilns resorting to various coal materials as a reducing agent, and in which a rst atmosphere in contact with the solid phase is of a reducing type, while a second atmosphere which is the actual gasiform phase is of a more or less oxidizing type. It is hardly necessary to mention the fact that the temperatures are readily adjustable throughout the length of my rotary kiln operating with reducing gases. This forms an interesting-feature of the kiln which allows executing various reductions of ore under the best conditions of thermodynamic eiciency and cost;

My invention is by no means limited to the embodiment which has just been described and it covers all the modifications thereof falling within the scope of the accompanying claims.

What I claim is t 1. A rotary ore-reducing kiln operating with a'supply of reducing gases, comprising a main elongated rotary chamber including end portions and a medial portion therebetween, an outer jacket surrounding said chamber, rigid with the latter and dening a closed passageway between itself and said chamber throughout the length of the latter, means for feeding ore into one end portion of the chamber, means for removing the metal obtained upon reduction of the ore inside the kiln out of the other portion of said chamber, means `for feeding a reducing gas from the supply through both ends of the passageway formed by the jacket over the outer wall of the chamber towards the medial part of said passageway registering with the medial portion of the chamber, nozzles connecting said medial section of the jacket with the medial portion of the elongated chamber through the wall of the latter to feed reducing 4gases from both ends of the passageway, into said medial portion of the passageway, means for feeding oxygen-containing gases into said nozzles together with the reducing gases to burn the latter in the medial portion of the chamber and to thereby recover the heat of said reducing gases in said medial portion of the chamber, means for diverting a fraction of the reducing gases from the supply into said other end portion of the chamber to ow in counter-current relationship with the ore to be treated thereby, means for removing the reacted gases out of the first-mentioned end portion of said chamber, and means for regenerating the gases removed from the last-mentioned end portion and recycling same into the means feeding the reducing gases into the ends of the passageway in the jacket and into said other end of the chamber.

2. A rotary ore-reducing kiln operating with a supply of reducing gases, comprising a main elongated rotary chamber including end portions and a medial portion therebetween, annular transverse partitions subdividing the chamber into a plurality of interconnected compartments, means for rotating slowly the chamber, an outer jacket surrounding said chamber, rigid with the latter and deiining a closed passageway between itself and said chamber, throughout the length of the latter, means for feeding ore into one end portion of the chamber, means for removing the metal obtained upon reduction of the ore inside the kiln out of the other end portion of said chamber, means for feeding a reducing gas from the supply through both ends of the passageway formed by the jacket over the outer wall of the chamber towards the medial part of said passageway registering with the medial portion of the chamber, nozzles connecting said medial section of the jacket with the corresponding compartments in the medial portion of the elongated member through the wall of the latter to feed the reducing gases from both ends of the passageway into said medial portion of the passageway, means for feeding oxygen-containing gases into said nozzles together with the reducing gases to burn the latter in the medial portion of the chamber and to thereby recover the heat of said reducing gases in said medial portion of the chamber, means for diverting a fmction of the reducing gases from the supply into said other end portion of the chamber to flow in counter-current relationship with the ore to be treated, and means for removing the reacted gases out of the first-mentioned end portion of said chamber.

3. A rotary ore-reducing kiln operating with a supply of reducing gases, comprising a main elongated rotary chamber including end portions and a medial portion therebetween, annular transverse partitions subdividing the chamber into a plurality of interconnected compartments, means for rotating `slowly the chamber, an outer jacket surrounding said chamber, rigid with the latter and defining a closed passageway between itself and said chamber, throughout the length of the latter, three :rotary joints in coaxial registry with the extremity of each outer portion of the chamber, means for feeding ore through one rotary joint into one end portion of the chamber, means for removing the metal obtained upon treatment of the ore through a rotary joint out of the other end portion of said chamber, means for feeding a reducing gas from the supply through fulther corresponding rotary joints into both ends of the passageway formed by the iacket over the outer wall of the chamber towards the medial part of said passageway registering with the medial portion of theV chamber, nozzles connecting said medial section of the jacket with the medial portion of the elongated chamber through the wall of the latter to feed the reducing gases from both ends of the passageway into said medial portion of the passageway, means for introduoing oxygen-containing gases through the third rotary joint registering with the other end portion or" the chamber into said nozzles to mix with the reducing gases fed into the latter, to burn said gases, means for diverting a fraction of the reducing gases passing through the corresponding rotary joint into said other end portion of the chamber to dow in counter-current relationship with the ore to be treated thereby, mems for removing the reacted gases out of the third rotary joint at said first-mentionedend of the chamber, and means for regenerating the gases removed from last-mentioned rotary joint and recycling same into the two further rotary joints.

References Cited in the le of this patent UNITED STATES PATENTS 236,648 Thompson Jan. 11, 1881 1,760,078 Newkirk et al. May 27, 1930 1,829,438 Coley Oct. 27, 1931 2,430,171 Hatch Nov. 4, 1947 2,507,123 Sproule et al. May 9, 1950 2,754,197 Wienert July 10, 1956 2,829,042 Moklebust Apr. 1, 1958 

